Bedford Borough Strategic Flood Risk Assessment Level 1
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Bedford Borough Strategic Flood Risk Assessment Level 1 Bedford Borough Strategic Flood Risk Assessment – Level 1 Notice This report was produced by Atkins Limited for Bedford Borough Council for the specific purpose of the Bedford Borough Strategic Flood Risk Assessment. This report may not be used by any person other than Bedford Borough Council without Bedford Borough Council’s express permission. In any event, Atkins accepts no liability for any costs, liabilities or losses arising as a result of the use of or reliance upon the contents of this report by any person other than Bedford Borough Council. Atkins Limited Document History JOB NUMBER AND REFERENCE: DOCUMENT REF: Bedford SFRA v1.4 - Level 1.doc 5061078/72/DG/054 1.4 FINAL CN/JL KP TR CN July 2008 1.3 Final for Review CN KP TR CN June 2008 1.2 Final for Review JL KP TR JL May 2008 1.1 Final for Client Review JL KP TR JL May 2008 1 Draft for Client Review TG, JL KP TR, SF JL March 2008 Revision Purpose Description Originated Checked Reviewed Authorised Date 5061078/Bedford SFRA v1.4 - Level 1.doc 5061078/Bedford SFRA v1.4 - Level 1.doc Bedford Borough Strategic Flood Risk Assessment Contents Section Page Glossary of Terms 3 Non Technical Summary 5 1. Introduction 7 1.1 Need for a Strategic Flood Risk Assessment 7 1.2 Scope of the Document 7 2. Planning Policy Relating to Flood Risk 9 2.1 National Planning Policy 9 2.2 Local Planning Policy Relating to Flood Risk 11 3. Data Collection and Review 15 3.1 Consultation 15 3.2 Catchment Characteristics 16 3.3 Sources of Flood Risk Data 16 3.4 Data Summary 24 4. Flood Risk 27 4.1 Sources of Flooding 27 4.2 Flood Defences 30 4.3 Flood Risk Sensitivity 30 5. Developer Guidance 35 5.1 Generic Developer Guidance 35 5.2 Site Specific Information for Developers 41 6. Conclusions and Recommendations 45 6.1 Conclusions 45 6.2 Recommendations for the Level 2 SFRA 46 References 49 List of Tables Table 2.1 – Bedford Borough Local Plan and Local Policies: Policies relating to flood risk 11 Table 2.2 – East of England Plan: Policy SS14 Development and Flood Risk 12 Table 2.3 – East of England Plan: Policy WAT 4 Flood Risk Management 12 Table 2.4 - MKSMSRS: Strategic Policy 3 Sustainable Communities 13 Table 3.1 –Hydraulic Model Summary 18 Table 3.2 – Anglian Water’s DG5 register: Key locations and type of sewer 18 Table 3.3 - Flood Risk Vulnerability Classification (based on Table D2 of PPS25) 21 Table 3.4 – Appropriate Development for each Flood Zone (based on Table D3 of PPS25) 22 Table 4.1 – SUDS Options that may be utilised within Bedford Borough 31 Table 6.1 – Recommended further hydraulic modelling 46 Appendices Appendix A Bedford Borough Mapping 5061078/Bedford SFRA v1.4 - Level 1.doc 1 Bedford Borough Strategic Flood Risk Assessment A.1 Location Overview A.2 Development Allocations – excluding allocations within the TCAAP A.3 Flood Risk Overview – Environment A.4 Assets and Structures Overview A.5 Flood Warning Overview A.6 Bedford IDB Catchment A.7 Detailed Mapping – Index Map A.8 Detailed Flood Risk Mapping A.9 Detailed Assets and Structures Mapping Appendix B B.1 Anglian Water DG5 Register B.2 IDB Flood Defence Structures (Summary Table) 5061078/Bedford SFRA v1.4 - Level 1.doc 2 Bedford Borough Strategic Flood Risk Assessment Glossary of Terms Term Meaning / Definition AAD Average Annual Damages AEP Annual Exceedance Probability AFFMS Anglian Flow Forecasting Modelling System CFMP Catchment Flood Management Plan CSRIP Core Strategy & Rural Issues Plan DG5 Water companies record of Sewer Flooding LDDs Local Development Documents LDF Local Development Framework LPA Local Planning Authority FWD Flood Warnings Direct FRA Flood Risk Assessment FSR Flood Studies Report GIS Geographical Information System Main River This term is used for watercourses shown on statutory maps held by the Environment Agency and DEFRA. They can include any structure or appliance for controlling or regulating the flow of water into, in or out of the channel. The Environment Agency has permissive powers to carry out works of maintenance and improvement on these watercourses (Main Rivers). MKSMSRS Milton Keynes and South Midlands Sub-Regional Strategy NFCDD National Flood and Coastal Defence Database PPS1 Planning Policy Statement 1: Delivering Sustainable Development PPS3 Planning Policy Statement 3: Housing PPS25 Planning Policy Statement 25: Development and Flood Risk RFRA Regional Flood Risk Assessment RPB Regional Planning Boards RSS Regional Spatial Strategy SFRA Strategic Flood Risk Assessment SMD Soil Moisture Deficit SOP Standard of Protection SUDs Sustainable Drainage Systems TCAAP Bedford Town Centre Area Action Plan 5061078/Bedford SFRA v1.4 - Level 1.doc 3 Bedford Borough Strategic Flood Risk Assessment Annual Exceedance Probability (AEP) The severity of the events discussed in this document are defined as Annual Exceedance Probabilities (AEP), the table below provides a summary of AEP and corresponding Return Periods. The AEP is the probability that there will be an event exceeding a particular severity in any one year. The Return Period is the average duration (in years) between events of a particular severity. Annual Exceedance Probability Return Period 50% 1 in 2yrs 10% 1 in 10yrs 4% 1 in 25yrs 3.3% 1 in 30yrs 2% 1 in 50yrs 1.33% 1 in 75yrs 1% 1 in 100yrs 0.5% 1 in 200yrs 0.4% 1 in 250yrs 0.1% 1 in 1000yrs 5061078/Bedford SFRA v1.4 - Level 1.doc 4 Bedford Borough Strategic Flood Risk Assessment Non Technical Summary This Level 1 Strategic Flood Risk Assessment (SFRA) has been produced for the Bedford Borough Council. It compliments the Bedford Town SFRA completed by WSP in 2006, and should be read in conjunction with this document. An SFRA is required under Planning Policy Statement 25: Development and Flood Risk, to facilitate sustainable planning and development on a regional scale. In producing this document, consultation with a number of parties has taken place. The key consultees utilised in the completion of this Level 1 SFRA have been the Environment Agency, Anglian Water, Bedford Borough Council and the Bedford Group of Internal Drainage Boards (IDB). The data collected during this Level 1 SFRA has resulted in a high level of understanding of flood risk within the Bedford Borough. The main source of flood risk within the Bedford Borough is fluvial flooding from the River Gt. Ouse, which runs from west to east across the centre of the Bedford Borough. There are also areas of flood risk within the north of the Bedford Borough from the River Til, Riseley Brook and Pertenhall Brook, all of which are main rivers maintained by the Environment Agency. To the south-east of Bedford Borough lie many watercourses maintained by the IDB, all of which have the potential to cause fluvial flood risk. Some locations within the Bedford Borough are also at risk from surface water and foul water flooding. There is no evidence of groundwater flooding or flooding from the many balancing ponds that are located within the Bedford Borough, however the IDB and the Environment Agency have identified potential areas at risk from groundwater flooding which will be further investigated in the Level 2 SFRA. There are no British Waterway owned canals within the Bedford Borough; however there are plans to develop a canalised section of waterway between Milton Keynes and Bedford. These proposals will be assessed in more detail during the Level 2 SFRA. Bedford Borough Council has already allocated a series of development sites within the Borough. These sites have been subject to site specific FRAs and have been committed to development. This Level 1 SFRA does not focus on already allocated sites, and further information on these sites can be found in the site specific FRAs that have been completed for them. This Level 1 SFRA, has highlighted the areas that are at risk of flooding within Bedford Borough. The ‘Key Service Centres’ that Bedford Borough have identified for future development, have also been assessed in terms of flood risk. In the development of this Level 1 SFRA, a series of assumptions have been developed. These assumptions were developed in conjunction with Bedford Borough Council, the Environment Agency and the Bedford Group of Drainage Boards and are listed below: • all areas at risk of flooding are undefended; • the Functional Floodplain has been classed as any area lying within Flood Zone 3; and • the climate change outline is taken to be the same as the current Flood Zone 2 outline. The outcome of this Level 1 SFRA has enabled a series of recommendations to be developed, which upon approval of this Level 1 SFRA will form a detailed proposal and methodology for the Level 2 SFRA. 5061078/Bedford SFRA v1.4 - Level 1.doc 5 Bedford Borough Strategic Flood Risk Assessment Page left intentionally blank 5061078/Bedford SFRA v1.4 - Level 1.doc 6 Bedford Borough Strategic Flood Risk Assessment 1. Introduction 1.1 Need for a Strategic Flood Risk Assessment Planning Policy Statement 25 Development and Flood Risk (Refs. 1, 2) outlines the principles by which the government seeks to reduce the risk of flooding to new developments. This is achieved through a variety of tools, primarily based on the site specific Flood Risk Assessment (FRA) for proposed developments. To facilitate catchment-wide development, larger scale FRAs are required. These are in the form of Regional Flood Risk Assessments (RFRAs) and Strategic Flood Risk Assessments (SFRAs). An SFRA provides the information necessary to perform the Sequential Test for a region.